Many important biological investigations require the identification of proteins separated on one- and two-dimensional electrophoretic gels. For these studies, we have previously used the strategy of blotting the protein of interest to a membrane, enzymatic digestion on the membrane, followed by mass spectrometric analysis of the eluted peptides. To improve the ease, speed, and sensitivity of the analysis, we are devising methods for digestion of the protein in the gel itself, followed by direct elution of the resulting peptides from the gel. Various methods for visualization of the gel spots on the sample are being tested for sensitivity and ease of destaining. A paper describing the results of our development has been published (Qin et al., Anal. Chem. 69 (1997) 3995-4001.